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Micromachines, Volume 11, Issue 4 (April 2020) – 112 articles

Cover Story (view full-size image): We experimentally and theoretically established a rational design principle of a hydrogel/elastomer bilayer and further optimized it for a wide-field retinal electrode array. We manipulated the initial monomer concentrations of the pre-gel solutions to investigate its effect on the curvature. Then, we demonstrated stimuli-responsive transformation of a flower-shaped bilayer from a flat film to a curved 3D structure. View this paper
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Article
Polymer-Based Functional Cantilevers Integrated with Interdigitated Electrode Arrays—A Novel Platform for Cardiac Sensing
Micromachines 2020, 11(4), 450; https://doi.org/10.3390/mi11040450 - 24 Apr 2020
Cited by 3 | Viewed by 1225
Abstract
Heart related ailments are some of the most common causes for death in the world, and some of the causes are cardiac toxicity due to drugs. Several platforms have been developed in this regard over the years that can measure electrical or mechanical [...] Read more.
Heart related ailments are some of the most common causes for death in the world, and some of the causes are cardiac toxicity due to drugs. Several platforms have been developed in this regard over the years that can measure electrical or mechanical behavior of cardiomyocytes. In this study, we have demonstrated a biomedical device that can simultaneously measure electrophysiology and contraction force of cardiomyocytes. This dual-function device is composed of a photosensitive polymer-based cantilever, with a pair of metal-based interdigitated electrodes on its surface, such that the cantilever can measure the contraction force of cardiomyocytes and the electrodes can measure the impedance between cells and substrate. The cantilever is patterned with microgrooves so that the cardiomyocytes can align to the cantilever in order to make a higher cantilever deflection in response to contraction force. Preliminary experimental results have identified the potential for use in the drug-induced cardiac toxicity tests, and further optimization is desirable to extend the technique to various bio-sensor areas. Full article
(This article belongs to the Special Issue Selected Papers from the ICAE 2019)
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Review
Nonlinear Optics in Dielectric Guided-Mode Resonant Structures and Resonant Metasurfaces
Micromachines 2020, 11(4), 449; https://doi.org/10.3390/mi11040449 - 24 Apr 2020
Cited by 3 | Viewed by 1081
Abstract
Nonlinear optics is an important area of photonics research for realizing active optical functionalities such as light emission, frequency conversion, and ultrafast optical switching for applications in optical communication, material processing, precision measurements, spectroscopic sensing and label-free biological imaging. An emerging topic in [...] Read more.
Nonlinear optics is an important area of photonics research for realizing active optical functionalities such as light emission, frequency conversion, and ultrafast optical switching for applications in optical communication, material processing, precision measurements, spectroscopic sensing and label-free biological imaging. An emerging topic in nonlinear optics research is to realize high efficiency optical functionalities in ultra-small, sub-wavelength length scale structures by leveraging interesting optical resonances in surface relief metasurfaces. Such artificial surfaces can be engineered to support high quality factor resonances for enhanced nonlinear optical interaction by leveraging interesting physical mechanisms. The aim of this review article is to give an overview of the emerging field of nonlinear optics in dielectric based sub-wavelength periodic structures to realize efficient harmonic generators, wavelength mixers, optical switches etc. Dielectric metasurfaces support the realization of high quality-factor resonances with electric field concentrated either inside or in the vicinity of the dielectric media, while at the same time operate at high optical intensities without damage. The periodic dielectric structures considered here are broadly classified into guided-mode resonant structures and resonant metasurfaces. The basic physical mechanisms behind guided-mode resonances, electromagnetically-induced transparency like resonances and bound-states in continuum resonances in periodic photonic structures are discussed. Various nonlinear optical processes studied in such structures with example implementations are also reviewed. Finally, some future directions of interest in terms of realizing large-area metasurfaces, techniques for enhancing the efficiency of the nonlinear processes, heterogenous integration, and extension to non-conventional wavelength ranges in the ultra-violet and infrared region are discussed. Full article
(This article belongs to the Special Issue Nonlinear Photonics Devices)
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Review
Sperm Cell Driven Microrobots—Emerging Opportunities and Challenges for Biologically Inspired Robotic Design
Micromachines 2020, 11(4), 448; https://doi.org/10.3390/mi11040448 - 23 Apr 2020
Cited by 16 | Viewed by 4797
Abstract
With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are [...] Read more.
With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots—a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end. Full article
(This article belongs to the Special Issue Advances in Microswimmers)
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Article
Survival Rate of Cells Sent by a Low Mechanical Load Tube Pump: The “Ring Pump”
Micromachines 2020, 11(4), 447; https://doi.org/10.3390/mi11040447 - 23 Apr 2020
Cited by 1 | Viewed by 916
Abstract
A ring pump (RP) is a useful tool for microchannels and automated cell culturing. We have been developing RPs (a full-press ring pump, FRP; and a mid-press ring pump, MRP). However, damage to cells which were sent by the RP and the MRP [...] Read more.
A ring pump (RP) is a useful tool for microchannels and automated cell culturing. We have been developing RPs (a full-press ring pump, FRP; and a mid-press ring pump, MRP). However, damage to cells which were sent by the RP and the MRP was not investigated, and no other studies have compared the damage to cells between RPs and peristaltic pumps (PPs). Therefore, first, we evaluated the damage to cells that were sent by a small size FRP (s-FRP) and small size MRPs (s-MRPs; gap = 25 or 50 μm, respectively). “Small size” means that the s-FRP and the s-MRPs are suitable for microchannel-scale applications. The survival rate of cells sent by the s-MRPs was higher than those sent by the s-FRP, and less damage caused by the former. Second, we compared the survival rate of cells that were sent by a large size FRP (l-FRP), a large size MRP (l-MRP) (gap = 50 μm) and a PP. “Large size” means that the l-FRP and the l-MRP are suitable for automated cell culture system applications. We could not confirm any differences among the cell survival rates. On the other hand, when cells suspended in Dulbecco’s phosphate-buffered saline solution were circulated with the l-MRP (gap = 50 μm) and the PP, we confirmed a difference in cell survival rate, and less damage caused by the former. Full article
(This article belongs to the Special Issue Microfluidic Platforms for Cell Culture and Investigations)
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Article
Semi-Automated Extraction of the Distribution of Single Defects for nMOS Transistors
Micromachines 2020, 11(4), 446; https://doi.org/10.3390/mi11040446 - 23 Apr 2020
Cited by 4 | Viewed by 777
Abstract
Miniaturization of metal-oxide-semiconductor field effect transistors (MOSFETs) is typically beneficial for their operating characteristics, such as switching speed and power consumption, but at the same time miniaturization also leads to increased variability among nominally identical devices. Adverse effects due to oxide traps in [...] Read more.
Miniaturization of metal-oxide-semiconductor field effect transistors (MOSFETs) is typically beneficial for their operating characteristics, such as switching speed and power consumption, but at the same time miniaturization also leads to increased variability among nominally identical devices. Adverse effects due to oxide traps in particular become a serious issue for device performance and reliability. While the average number of defects per device is lower for scaled devices, the impact of the oxide defects is significantly more pronounced than in large area transistors. This combination enables the investigation of charge transitions of single defects. In this study, we perform random telegraph noise (RTN) measurements on about 300 devices to statistically characterize oxide defects in a Si/SiO 2 technology. To extract the noise parameters from the measurements, we make use of the Canny edge detector. From the data, we obtain distributions of the step heights of defects, i.e., their impact on the threshold voltage of the devices. Detailed measurements of a subset of the defects further allow us to extract their vertical position in the oxide and their trap level using both analytical estimations and full numerical simulations. Contrary to published literature data, we observe a bimodal distribution of step heights, while the extracted distribution of trap levels agrees well with recent studies. Full article
(This article belongs to the Special Issue Miniaturized Transistors, Volume II)
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Review
DNA Microsystems for Biodiagnosis
Micromachines 2020, 11(4), 445; https://doi.org/10.3390/mi11040445 - 23 Apr 2020
Cited by 1 | Viewed by 1347
Abstract
Researchers are continuously making progress towards diagnosis and treatment of numerous diseases. However, there are still major issues that are presenting many challenges for current medical diagnosis. On the other hand, DNA nanotechnology has evolved significantly over the last three decades and is [...] Read more.
Researchers are continuously making progress towards diagnosis and treatment of numerous diseases. However, there are still major issues that are presenting many challenges for current medical diagnosis. On the other hand, DNA nanotechnology has evolved significantly over the last three decades and is highly interdisciplinary. With many potential technologies derived from the field, it is natural to begin exploring and incorporating its knowledge to develop DNA microsystems for biodiagnosis in order to help address current obstacles, such as disease detection and drug resistance. Here, current challenges in disease detection are presented along with standard methods for diagnosis. Then, a brief overview of DNA nanotechnology is introduced along with its main attractive features for constructing biodiagnostic microsystems. Lastly, suggested DNA-based microsystems are discussed through proof-of-concept demonstrations with improvement strategies for standard diagnostic approaches. Full article
(This article belongs to the Special Issue Biosensors and MEMS-based Diagnostic Applications)
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Article
Generation of Ultra-Thin-Shell Microcapsules Using Osmolarity-Controlled Swelling Method
Micromachines 2020, 11(4), 444; https://doi.org/10.3390/mi11040444 - 23 Apr 2020
Cited by 1 | Viewed by 868
Abstract
Microcapsules are attractive core-shell configurations for studies of controlled release, biomolecular sensing, artificial microbial environments, and spherical film buckling. However, the production of microcapsules with ultra-thin shells remains a challenge. Here we develop a simple and practical osmolarity-controlled swelling method for the mass [...] Read more.
Microcapsules are attractive core-shell configurations for studies of controlled release, biomolecular sensing, artificial microbial environments, and spherical film buckling. However, the production of microcapsules with ultra-thin shells remains a challenge. Here we develop a simple and practical osmolarity-controlled swelling method for the mass production of monodisperse microcapsules with ultra-thin shells via water-in-oil-in-water (W/O/W) double-emulsion drops templating. The size and shell thickness of the double-emulsion drops are precisely tuned by changing the osmotic pressure between the inner cores and the suspending medium, indicating the practicability and effectiveness of this swelling method in tuning the shell thickness of double-emulsion drops and the resultant microcapsules. This method enables the production of microcapsules even with an ultra-thin shell less than hundreds of nanometers, which overcomes the difficulty in producing ultra-thin-shell microcapsules using the classic microfluidic emulsion technologies. In addition, the ultra-thin-shell microcapsules can maintain their intact spherical shape for up to 1 year without rupturing in our long-term observation. We believe that the osmolarity-controlled swelling method will be useful in generating ultra-thin-shell polydimethylsiloxane (PDMS) microcapsules for long-term encapsulation, and for thin film folding, buckling and rupturing investigation. Full article
(This article belongs to the Special Issue Droplet Microfluidics)
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Article
Rheology of a Dilute Suspension of Aggregates in Shear-Thinning Fluids
Micromachines 2020, 11(4), 443; https://doi.org/10.3390/mi11040443 - 22 Apr 2020
Cited by 1 | Viewed by 810
Abstract
The prediction of the viscosity of suspensions is of fundamental importance in several fields. Most of the available studies have been focused on particles with simple shapes, for example, spheres or spheroids. In this work, we study the viscosity of a dilute suspension [...] Read more.
The prediction of the viscosity of suspensions is of fundamental importance in several fields. Most of the available studies have been focused on particles with simple shapes, for example, spheres or spheroids. In this work, we study the viscosity of a dilute suspension of fractal-shape aggregates suspended in a shear-thinning fluid by direct numerical simulations. The suspending fluid is modeled by the power-law constitutive equation. For each morphology, a map of particle angular velocities is obtained by solving the governing equations for several particle orientations. The map is used to integrate the kinematic equation for the orientation vectors and reconstruct the aggregate orientational dynamics. The intrinsic viscosity is computed by a homogenization procedure along the particle orbits. In agreement with previous results on Newtonian suspensions, the intrinsic viscosity, averaged over different initial orientations and aggregate morphologies characterized by the same fractal parameters, decreases by increasing the fractal dimension, that is, from rod-like to spherical-like aggregates. Shear-thinning further reduces the intrinsic viscosity showing a linear dependence with the flow index in the investigated range. The intrinsic viscosity can be properly scaled with respect to the number of primary particles and the flow index to obtain a single curve as a function of the fractal dimension. Full article
(This article belongs to the Special Issue Rheology and Complex Fluid Flows in Microfluidics)
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Article
Scalable Parallel Manipulation of Single Cells Using Micronozzle Array Integrated with Bidirectional Electrokinetic Pumps
Micromachines 2020, 11(4), 442; https://doi.org/10.3390/mi11040442 - 22 Apr 2020
Viewed by 810
Abstract
High throughput reconstruction of in vivo cellular environments allows for efficient investigation of cellular functions. If one-side-open multi-channel microdevices are integrated with micropumps, the devices will achieve higher throughput in the manipulation of single cells while maintaining flexibility and open accessibility. This paper [...] Read more.
High throughput reconstruction of in vivo cellular environments allows for efficient investigation of cellular functions. If one-side-open multi-channel microdevices are integrated with micropumps, the devices will achieve higher throughput in the manipulation of single cells while maintaining flexibility and open accessibility. This paper reports on the integration of a polydimethylsiloxane (PDMS) micronozzle array and bidirectional electrokinetic pumps driven by DC-biased AC voltages. Pt/Ti and indium tin oxide (ITO) electrodes were used to study the effect of DC bias and peak-to-peak voltage and electrodes in a low conductivity isotonic solution. The flow was bidirectionally controlled by changing the DC bias. A pump integrated with a micronozzle array was used to transport single HeLa cells into nozzle holes. The application of DC-biased AC voltage (100 kHz, 10 Vpp, and VDC: −4 V) provided a sufficient electroosmotic flow outside the nozzle array. This integration method of nozzle and pumps is anticipated to be a standard integration method. The operating conditions of DC-biased AC electrokinetic pumps in a biological buffer was clarified and found useful for cell manipulation. Full article
(This article belongs to the Special Issue Micro/Nanofluidic Devices for Single Cell Analysis, Volume II)
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Article
Electrospun Fibers and Sorbents as a Possible Basis for Effective Composite Wound Dressings
Micromachines 2020, 11(4), 441; https://doi.org/10.3390/mi11040441 - 22 Apr 2020
Cited by 6 | Viewed by 1553
Abstract
Skin burns and ulcers are considered hard-to-heal wounds due to their high infection risk. For this reason, designing new options for wound dressings is a growing need. The objective of this work is to investigate the properties of poly (ε-caprolactone)/poly (vinyl-pyrrolidone) (PCL/PVP) microfibers [...] Read more.
Skin burns and ulcers are considered hard-to-heal wounds due to their high infection risk. For this reason, designing new options for wound dressings is a growing need. The objective of this work is to investigate the properties of poly (ε-caprolactone)/poly (vinyl-pyrrolidone) (PCL/PVP) microfibers produced via electrospinning along with sorbents loaded with Argovit™ silver nanoparticles (Ag-Si/Al2O3) as constituent components for composite wound dressings. The physicochemical properties of the fibers and sorbents were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and inductively coupled plasma optical emission spectroscopy (ICP-OES). The mechanical properties of the fibers were also evaluated. The results of this work showed that the tested fibrous scaffolds have melting temperatures suitable for wound dressings design (58–60 °C). In addition, they demonstrated to be stable even after seven days in physiological solution, showing no macroscopic damage due to PVP release at the microscopic scale. Pelletized sorbents with the higher particle size demonstrated to have the best water uptake capabilities. Both, fibers and sorbents showed antimicrobial activity against Gram-negative bacteria Pseudomona aeruginosa and Escherichia coli, Gram-positive Staphylococcus aureus and the fungus Candida albicans. The best physicochemical properties were obtained with a scaffold produced with a PCL/PVP ratio of 85:15, this polymeric scaffold demonstrated the most antimicrobial activity without affecting the cell viability of human fibroblast. Pelletized Ag/Si-Al2O3-3 sorbent possessed the best water uptake capability and the higher antimicrobial activity, over time between all the sorbents tested. The combination of PCL/PVP 85:15 microfibers with the chosen Ag/Si-Al2O3-3 sorbent will be used in the following work for creation of wound dressings possessing exudate retention, biocompatibility and antimicrobial activity. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication of Polymers for Regenerative Medicine)
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Article
High-Throughput Particle Concentration Using Complex Cross-Section Microchannels
Micromachines 2020, 11(4), 440; https://doi.org/10.3390/mi11040440 - 22 Apr 2020
Cited by 1 | Viewed by 1139
Abstract
High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency [...] Read more.
High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency and a confinement ratio less than 0.07. Particle focusing in our microfluidic system was observed in a single, tight focusing line, in which higher particle concentration is possible, as compared with simple rectangular or trapezoidal cross-sections with similar flow area. The sharper focusing stems from the confinement of Dean vortices in the trapezoidal region of the complex cross-section. To quantify this effect, we introduce a new parameter, complex focusing number or CFN, which is indicative of the enhancement of inertial focusing of particles in these channels. Three spiral microchannels with various widths of 400 µm, 500 µm, and 600 µm, with the corresponding CFNs of 4.3, 4.5, and 6, respectively, were used. The device with the total width of 600 µm was shown to have a separation efficiency of ~98%, and by recirculating, the output concentration of the sample was 500 times higher than the initial input. Finally, the investigation of results showed that the magnitude of CFN relies entirely on the microchannel geometry, and it is independent of the overall width of the channel cross-section. We envision that this concept of particle focusing through complex cross-sections will prove useful in paving the way towards more efficient inertial microfluidic devices. Full article
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Article
Ultrasensitive Stress Biomarker Detection Using Polypyrrole Nanotube Coupled to a Field-Effect Transistor
Micromachines 2020, 11(4), 439; https://doi.org/10.3390/mi11040439 - 22 Apr 2020
Cited by 2 | Viewed by 925
Abstract
Stress biomarkers such as hormones and neurotransmitters in bodily fluids can indicate an individual’s physical and mental state, as well as influence their quality of life and health. Thus, sensitive and rapid detection of stress biomarkers (e.g., cortisol) is important for management of [...] Read more.
Stress biomarkers such as hormones and neurotransmitters in bodily fluids can indicate an individual’s physical and mental state, as well as influence their quality of life and health. Thus, sensitive and rapid detection of stress biomarkers (e.g., cortisol) is important for management of various diseases with harmful symptoms, including post-traumatic stress disorder and depression. Here, we describe rapid and sensitive cortisol detection based on a conducting polymer (CP) nanotube (NT) field-effect transistor (FET) platform. The synthesized polypyrrole (PPy) NT was functionalized with the cortisol antibody immunoglobulin G (IgG) for the sensitive and specific detection of cortisol hormone. The anti-cortisol IgG was covalently attached to a basal plane of PPy NT through an amide bond between the carboxyl group of PPy NT and the amino group of anti-cortisol IgG. The resulting field-effect transistor-type biosensor was utilized to evaluate various cortisol concentrations. Cortisol was sensitively measured to a detection limit of 2.7 × 10−10 M (100 pg/mL), with a dynamic range of 2.7 × 10−10 to 10−7 M; it exhibited rapid responses (<5 s). We believe that our approach can serve as an alternative to time-consuming and labor-intensive health questionnaires; it can also be used for diagnosis of underlying stress-related disorders. Full article
(This article belongs to the Special Issue Conductive Nanomaterial-Based Chem/Bio Sensors)
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Brief Report
Hybrid Internal Combustion Engine Based Auxiliary Power Unit
Micromachines 2020, 11(4), 438; https://doi.org/10.3390/mi11040438 - 21 Apr 2020
Cited by 2 | Viewed by 673
Abstract
The brief presents some principles of the ON/OFF operational strategy applied to energy management of a hybrid internal combustion engine (ICE) based auxiliary power unit (APU). It is shown that significant reduction of fuel consumption (78% for the example system presented) and maintenance [...] Read more.
The brief presents some principles of the ON/OFF operational strategy applied to energy management of a hybrid internal combustion engine (ICE) based auxiliary power unit (APU). It is shown that significant reduction of fuel consumption (78% for the example system presented) and maintenance expenses (80% operation time decrease was attained by the system) may be achieved by such a strategy, shifting the system operation point towards corresponding optimal region. The side effect of aggravated amount of starting events is cured by employing an actively balanced supercapacitor (SC)-based emergency starter (SCS). The SCS operates as short-time energy storage device, charging from the battery at a low rate and then providing a current burst required for proper internal combustion engine starting. Current sensorless method of automatic connection (based on bus voltage sensing) and disconnection (based on sensing the voltage across bidirectional MOSFET-based switch) of the SCS is also proposed. The proposed circuitry, successfully validated by experiments, may be arbitrarily scaled up or down according to application rating. Full article
(This article belongs to the Special Issue Miniaturized Generators)
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Communication
Randomly Multiplexed Diffractive Lens and Axicon for Spatial and Spectral Imaging
Micromachines 2020, 11(4), 437; https://doi.org/10.3390/mi11040437 - 21 Apr 2020
Cited by 9 | Viewed by 1148
Abstract
A new hybrid diffractive optical element (HDOE) was designed by randomly multiplexing an axicon and a Fresnel zone lens. The HDOE generates two mutually coherent waves, namely a conical wave and a spherical wave, for every on-axis point object in the object space. [...] Read more.
A new hybrid diffractive optical element (HDOE) was designed by randomly multiplexing an axicon and a Fresnel zone lens. The HDOE generates two mutually coherent waves, namely a conical wave and a spherical wave, for every on-axis point object in the object space. The resulting self-interference intensity distribution is recorded as the point spread function. A library of point spread functions are recorded in terms of the different locations and wavelengths of the on-axis point objects in the object space. A complicated object illuminated by a spatially incoherent multi-wavelength source generated an intensity pattern that was the sum of the shifted and scaled point spread intensity distributions corresponding to every spatially incoherent point and wavelength in the complicated object. The four-dimensional image of the object was reconstructed using computer processing of the object intensity distribution and the point spread function library. Full article
(This article belongs to the Special Issue Micro/Nano-surfaces: Fabrication and Applications)
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Article
A 3D Printed Self-Sustainable Cell-Encapsulation Drug Delivery Device for Periocular Transplant-Based Treatment of Retinal Degenerative Diseases
Micromachines 2020, 11(4), 436; https://doi.org/10.3390/mi11040436 - 21 Apr 2020
Cited by 1 | Viewed by 1531
Abstract
Self-sustainable release of brain-derived neurotrophic factor (BDNF) to the retina using minimally invasive cell-encapsulation devices is a promising approach to treat retinal degenerative diseases (RDD). Herein, we describe such a self-sustainable drug delivery device with human retinal pigment epithelial (ARPE-19) cells (cultured on [...] Read more.
Self-sustainable release of brain-derived neurotrophic factor (BDNF) to the retina using minimally invasive cell-encapsulation devices is a promising approach to treat retinal degenerative diseases (RDD). Herein, we describe such a self-sustainable drug delivery device with human retinal pigment epithelial (ARPE-19) cells (cultured on collagen coated polystyrene (PS) sheets) enclosed inside a 3D printed semi-porous capsule. The capsule was 3D printed with two photo curable polymers: triethylene glycol dimethacrylate (TEGDM) and polyethylene glycol dimethylacrylate (PEGDM). The capsule’s semi-porous membrane (PEGDM) could serve three functions: protecting the cells from body’s immune system by limiting diffusion (5.97 ± 0.11%) of large molecules like immunoglobin G (IgG)(150 kDa); helping the cells to survive inside the capsule by allowing diffusion (43.20 ± 2.16%) of small molecules (40 kDa) like oxygen and necessary nutrients; and helping in the treatment of RDD by allowing diffusion of cell-secreted BDNF to the outside environment. In vitro results showed a continuous BDNF secretion from the device for at least 16 days, demonstrating future potential of the cell-encapsulation device for the treatment of RDD in a minimally invasive and self-sustainable way through a periocular transplant. Full article
(This article belongs to the Special Issue Advanced Drug Delivery Devices)
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Article
Low-Cost Battery-Powered and User-Friendly Real-Time Quantitative PCR System for the Detection of Multigene
Micromachines 2020, 11(4), 435; https://doi.org/10.3390/mi11040435 - 21 Apr 2020
Cited by 1 | Viewed by 968
Abstract
Real-time polymerase chain reaction (PCR) is the standard for nucleic acid detection and plays an important role in many fields. A new chip design is proposed in this study to avoid the use of expensive instruments for hydrophobic treatment of the surface, and [...] Read more.
Real-time polymerase chain reaction (PCR) is the standard for nucleic acid detection and plays an important role in many fields. A new chip design is proposed in this study to avoid the use of expensive instruments for hydrophobic treatment of the surface, and a new injection method solves the issue of bubbles formed during the temperature cycle. We built a battery-powered real-time PCR device to follow polymerase chain reaction using fluorescence detection and developed an independently designed electromechanical control system and a fluorescence analysis software to control the temperature cycle, the photoelectric detection coupling, and the automatic analysis of the experimental data. The microchips and the temperature cycling system cost USD 100. All the elements of the device are available through open access, and there are no technical barriers. The simple structure and manipulation allows beginners to build instruments and perform PCR tests after only a short tutorial. The device is used for analysis of the amplification curve and the melting curve of multiple target genes to demonstrate that our instrument has the same accuracy and stability as a commercial instrument. Full article
(This article belongs to the Special Issue Organs-on-chips, Volume II)
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Perspective
3D Printed MEMS Technology—Recent Developments and Applications
Micromachines 2020, 11(4), 434; https://doi.org/10.3390/mi11040434 - 20 Apr 2020
Cited by 13 | Viewed by 2936
Abstract
Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but [...] Read more.
Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but also in future autonomously driving cars. Most MEMS elements are based on silicon, which is not deformed plastically under a load, as opposed to metals. While highly sophisticated solutions were already found for diverse MEMS sensors, actuators, and other elements, MEMS fabrication is less standardized than pure microelectronics, which sometimes blocks new ideas. One of the possibilities to overcome this problem may be the 3D printing approach. While most 3D printing technologies do not offer sufficient resolution for MEMS production, and many of the common 3D printing materials cannot be used for this application, there are still niches in which the 3D printing of MEMS enables producing new structures and thus creating elements for new applications, or the faster and less expensive production of common systems. Here, we give an overview of the most recent developments and applications in 3D printing of MEMS. Full article
(This article belongs to the Special Issue 3D Printing of MEMS Technology)
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Article
Simulation Study of Surface Transfer Doping of Hydrogenated Diamond by MoO3 and V2O5 Metal Oxides
Micromachines 2020, 11(4), 433; https://doi.org/10.3390/mi11040433 - 20 Apr 2020
Cited by 3 | Viewed by 1369
Abstract
In this work, we investigate the surface transfer doping process that is induced between hydrogen-terminated (100) diamond and the metal oxides, MoO3 and V2O5, through simulation using a semi-empirical Density Functional Theory (DFT) method. DFT was used to [...] Read more.
In this work, we investigate the surface transfer doping process that is induced between hydrogen-terminated (100) diamond and the metal oxides, MoO3 and V2O5, through simulation using a semi-empirical Density Functional Theory (DFT) method. DFT was used to calculate the band structure and charge transfer process between these oxide materials and hydrogen terminated diamond. Analysis of the band structures, density of states, Mulliken charges, adsorption energies and position of the Valence Band Minima (VBM) and Conduction Band Minima (CBM) energy levels shows that both oxides act as electron acceptors and inject holes into the diamond structure. Hence, those metal oxides can be described as p-type doping materials for the diamond. Additionally, our work suggests that by depositing appropriate metal oxides in an oxygen rich atmosphere or using metal oxides with high stochiometric ration between oxygen and metal atoms could lead to an increase of the charge transfer between the diamond and oxide, leading to enhanced surface transfer doping. Full article
(This article belongs to the Special Issue Miniaturized Transistors, Volume II)
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Article
Design and Investigation of Modern UWB-MIMO Antenna with Optimized Isolation
Micromachines 2020, 11(4), 432; https://doi.org/10.3390/mi11040432 - 20 Apr 2020
Cited by 3 | Viewed by 1098
Abstract
This paper proposes a compact, semi-circular shaped multiple input multiple output (MIMO) antenna design with high isolation and enhanced bandwidth for ultrawide band (UWB) applications. A decoupling stub is used for high isolation reaching up to −55 dB over the entire bandwidth. The [...] Read more.
This paper proposes a compact, semi-circular shaped multiple input multiple output (MIMO) antenna design with high isolation and enhanced bandwidth for ultrawide band (UWB) applications. A decoupling stub is used for high isolation reaching up to −55 dB over the entire bandwidth. The proposed antenna is used for UWB as well as super wide band (SWB) applications. The overall size of the proposed antenna is 18 × 36 × 1.6   mm3. The | S 11 |   and voltage standing wave ratio (VSWR) of the proposed antenna are less than −10 dB and 2, respectively, in the range of 3–40 GHz. The total impedance bandwidth of the proposed design is 37 GHz. The VSWR, | S 11 | , | S 22 | , | S 21 | , | S 12 | , gain, envelope correlation coefficient (ECC), radiation pattern, and various other characteristic parameters are discussed in detail. The proposed antenna is optimized and simulated in a computer simulation technology (CST) studio, and printed on a FR4 substrate. Full article
(This article belongs to the Special Issue Future Wearable and Implants)
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Article
A Fluorescent Sensor-Assisted Paper-Based Competitive Lateral Flow Immunoassay for the Rapid and Sensitive Detection of Ampicillin in Hospital Wastewater
Micromachines 2020, 11(4), 431; https://doi.org/10.3390/mi11040431 - 20 Apr 2020
Cited by 2 | Viewed by 797
Abstract
In this study, a convenient assay method has been developed based on labeled functional nucleic acids (H-DNA) and a competitive fluorescent lateral flow immunoassay (CF-LFI) for ampicillin (AMP) detection. Herein, we designed the tunable AMP probes for AMP detection based on the AMP [...] Read more.
In this study, a convenient assay method has been developed based on labeled functional nucleic acids (H-DNA) and a competitive fluorescent lateral flow immunoassay (CF-LFI) for ampicillin (AMP) detection. Herein, we designed the tunable AMP probes for AMP detection based on the AMP aptamer, and the secondary DNA fragment. The probes can generate tunable signals on the test line (T line) and control line (C line) according to the concentration of AMP. The accuracy of detection was improved by optimizing the tunable AMP probes. Under the optimal conditions, the linear concentration of AMP detection is ranged from 10 to 200 ng/L with a limit of quantitation (LOQ) value of 2.71 ng/L, and the recovery is higher than 80.5 %. Moreover, the developed method shows the potential application for AMP detection in the hospital wastewater. Full article
(This article belongs to the Special Issue Micro Process-Devices)
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Article
Investigation of Hydrogen Embrittlement Susceptibility and Fracture Toughness Drop after in situ Hydrogen Cathodic Charging for an X65 Pipeline Steel
Micromachines 2020, 11(4), 430; https://doi.org/10.3390/mi11040430 - 20 Apr 2020
Cited by 3 | Viewed by 1101
Abstract
The present research focuses on the investigation of an in situ hydrogen charging effect during Crack Tip Opening Displacement testing (CTOD) on the fracture toughness properties of X65 pipeline steel. This grade of steel belongs to the broader category of High Strength Low [...] Read more.
The present research focuses on the investigation of an in situ hydrogen charging effect during Crack Tip Opening Displacement testing (CTOD) on the fracture toughness properties of X65 pipeline steel. This grade of steel belongs to the broader category of High Strength Low Alloy Steels (HSLA), and its microstructure consists of equiaxed ferritic and bainitic grains with a low volume fraction of degenerated pearlite islands. The studied X65 steel specimens were extracted from pipes with 19.15 mm wall thickness. The fracture toughness parameters were determined after imposing the fatigue pre-cracked specimens on air, on a specific electrolytic cell under a slow strain rate bending loading (according to ASTM G147-98, BS7448, and ISO12135 standards). Concerning the results of this study, in the first phase the hydrogen cations’ penetration depth, the diffusion coefficient of molecular and atomic hydrogen, and the surficial density of blisters were determined. Next, the characteristic parameters related to fracture toughness (such as J, KQ, CTODel, CTODpl) were calculated by the aid of the Force-Crack Mouth Open Displacement curves and the relevant analytical equations. Full article
(This article belongs to the Special Issue Advanced Manufacturing Technology)
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Article
Functionalization of Plastic Parts by Replication of Variable Pitch Laser-Induced Periodic Surface Structures
Micromachines 2020, 11(4), 429; https://doi.org/10.3390/mi11040429 - 20 Apr 2020
Cited by 4 | Viewed by 1095
Abstract
Surface functionalization of plastic parts has been studied and developed for several applications. However, demand for the development of reliable and profitable manufacturing strategies is still high. Here we develop and characterize a new process chain for the versatile and cost-effective production of [...] Read more.
Surface functionalization of plastic parts has been studied and developed for several applications. However, demand for the development of reliable and profitable manufacturing strategies is still high. Here we develop and characterize a new process chain for the versatile and cost-effective production of sub-micron textured plastic parts using laser ablation. The study includes the generation of different sub-micron structures on the surface of a mold using femtosecond laser ablation and vario-thermal micro-injection molding. The manufactured parts and their surfaces are characterized in consideration of polymer replication and wetting behavior. The results of the static contact angle measurements show that replicated Laser-Induced Periodic Surface Structures (LIPSSs) always increase the hydrophobicity of plastic parts. A maximum contact angle increase of 20% was found by optimizing the manufacturing thermal boundary conditions. The wetting behavior is linked to the transition from a Wenzel to Cassie–Baxter state, and is crucial in optimizing the injection molding cycle time. Full article
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Article
Experimental Characterization and Simulation of Thermoplastic Polymer Flow Hesitation in Thin-Wall Injection Molding Using Direct In-Mold Visualization Technique
Micromachines 2020, 11(4), 428; https://doi.org/10.3390/mi11040428 - 19 Apr 2020
Cited by 1 | Viewed by 1018
Abstract
A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to validate the simulation of the process with particular focus on [...] Read more.
A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to validate the simulation of the process with particular focus on the hesitation effect. The flow of the polymer was recorded at 500 frames per second using a high-speed camera (HSC). Two unfilled thermoplastic polymers, acrylonitrile butadiene styrene (ABS), and polypropylene (PP), were used to fill two different 50 mm × 18 mm staircase geometry cavities, which were specifically designed to evaluate the hesitation effect with thicknesses of 1500, 1250, 1000, 750, 500 µm (cavity insert no. 1) and 1500, 1200, 900, 600, 300 µm (cavity insert no. 2). In addition to the video recordings, the simulations were validated using the timings and the data obtained by three pressure sensors and two thermocouples located in the cavity. For each injection cycle recorded on camera the machine data were collected to carefully implement the correct boundary conditions in the simulations. The analysis of the video recordings highlighted that flow progression and hesitation were mainly influenced not only by the thickness, but also by the velocity and the material type. The simulation results were in relatively good agreement with the experiments in terms of flow pattern and progression. Filling times were predicted with an average relative error deviation of 2.5% throughout all the section thicknesses of the cavity. Lower accuracies in terms of both filling times and injection pressure were observed at increasingly thinner sections. Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Article
Improving the Recognition Accuracy of Memristive Neural Networks via Homogenized Analog Type Conductance Quantization
Micromachines 2020, 11(4), 427; https://doi.org/10.3390/mi11040427 - 18 Apr 2020
Viewed by 784
Abstract
Conductance quantization (QC) phenomena occurring in metal oxide based memristors demonstrate great potential for high-density data storage through multilevel switching, and analog synaptic weight update for effective training of the artificial neural networks. Continuous, linear and symmetrical modulation of the device conductance is [...] Read more.
Conductance quantization (QC) phenomena occurring in metal oxide based memristors demonstrate great potential for high-density data storage through multilevel switching, and analog synaptic weight update for effective training of the artificial neural networks. Continuous, linear and symmetrical modulation of the device conductance is a critical issue in QC behavior of memristors. In this contribution, we employ the scanning probe microscope (SPM) assisted electrode engineering strategy to control the ion migration process to construct single conductive filaments in Pt/HfOx/Pt devices. Upon deliberate tuning and evolution of the filament, 32 half integer quantized conductance states in the 16 G0 to 0.5 G0 range with enhanced distribution uniformity was achieved. Simulation results revealed that the numbers of the available QC states and fluctuation of the conductance at each state play an important role in determining the overall performance of the neural networks. The 32-state QC behavior of the hafnium oxide device shows improved recognition accuracy approaching 90% for handwritten digits, based on analog type operation of the multilayer perception (MLP) neural network. Full article
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Communication
mRNA as a Tool for Gene Transfection in 3D Cell Culture for Future Regenerative Therapy
Micromachines 2020, 11(4), 426; https://doi.org/10.3390/mi11040426 - 18 Apr 2020
Cited by 3 | Viewed by 1228
Abstract
A combination of three-dimensional (3D) cell culturing and non-viral gene transfection is promising in improving outcomes of cell transplantation therapy. Herein, gene transfection profiles in 3D cell culture were compared between plasmid DNA (pDNA) and messenger RNA (mRNA) introduction, using mesenchymal stem cell [...] Read more.
A combination of three-dimensional (3D) cell culturing and non-viral gene transfection is promising in improving outcomes of cell transplantation therapy. Herein, gene transfection profiles in 3D cell culture were compared between plasmid DNA (pDNA) and messenger RNA (mRNA) introduction, using mesenchymal stem cell (MSC) 3D spheroids. Green fluorescence protein (GFP) mRNA induced GFP protein expression in 77% of the cells in the spheroids, whereas only 34% of the cells became GFP positive following pDNA introduction. In mechanistic analyses, most of the cells in MSC spheroids were non-dividing, and pDNA failed to induce GFP expression in most of the non-dividing cells. In contrast, both dividing and non-dividing cells became GFP-positive after mRNA introduction, which led to a high overall percentage of GFP-positive cells in the spheroids. Consequently, mRNA encoding an osteogenic factor, runt-related transcription factor 2 (Runx2), allowed in vitro osteogenic differentiation of MSCs in spheroids more efficiently compared to Runx2 pDNA. Conclusively, mRNA exhibits high potential in gene transfection in 3D cell culture, in which the cell division rate is lower than that in monolayer culture, and the combination of mRNA introduction and 3D cell culture is a promising approach to improve outcomes of cell transplantation in future regenerative therapy. Full article
(This article belongs to the Special Issue Micro/Nano Devices in Biological Medicine)
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Article
Swelling Studies of Porous and Nonporous Semi-IPN Hydrogels for Sensor and Actuator Applications
Micromachines 2020, 11(4), 425; https://doi.org/10.3390/mi11040425 - 18 Apr 2020
Cited by 3 | Viewed by 724
Abstract
In this article, we present a semi-interpenetrating network (IPN) hydrogel of reasonable size with improved swelling behavior. The semi-IPN is composed of N-isopropylacrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid. Porosity was generated chemically by a surfactant-based template method. The swelling behavior was measured after an [...] Read more.
In this article, we present a semi-interpenetrating network (IPN) hydrogel of reasonable size with improved swelling behavior. The semi-IPN is composed of N-isopropylacrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid. Porosity was generated chemically by a surfactant-based template method. The swelling behavior was measured after an abrupt change of the temperature to 25 °C or 40 °C or after an abrupt change of the salt concentration of the aqueous medium surrounding the hydrogel samples. A set of static swelling degrees was determined from swelling measurements in salt solutions of varying concentrations and at different temperatures. Introducing porosity to the semi-IPN decreases the swelling times for most measurements while the sensor and actuator characteristics of the hydrogel found in previous studies are preserved. Additionally, we propose theoretical assumptions and explanations regarding the differences in the swelling kinetics of the porous and the nonporous semi-IPN and deduce implications for sensor and actuator applications. Full article
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Article
Blister Formation in Film Insert Moulding
Micromachines 2020, 11(4), 424; https://doi.org/10.3390/mi11040424 - 17 Apr 2020
Cited by 1 | Viewed by 760
Abstract
The formation of blister in the injection moulded parts, especially in the film insert moulded parts, is one of most significant causes of part rejection due to cosmetic requirements or functionality issues. The mechanism and physics of blister formation for molded parts are [...] Read more.
The formation of blister in the injection moulded parts, especially in the film insert moulded parts, is one of most significant causes of part rejection due to cosmetic requirements or functionality issues. The mechanism and physics of blister formation for molded parts are not well-understood by the state-of-the-art literature. The current paper increases the fundamental understanding of the causes for blister formation. In the experiment, a membrane strip of 5 mm in width was overmoulded with Polypropylene (PP), which formed a disc-shaped part with a diameter of 17.25 mm and a thickness of 500 µm. To investigate the influence of the processing parameters, a full factorial design of experiments (DoE) setup was conducted, including mould temperature (Tm), barrel temperature (Tb), injection speed (Vi) and packing pressure (Pp) as variables. The degree of blistering at the surface was characterized by the areal surface roughness parameters Spk and Smr1, measured with a confocal laser microscope. The measurements were taken on the 10 mm long section of the membrane surface in the centre of the moulded part across the entire width of the film. In addition, the film insert moulding (FIM)-process was simulated and the average shrinkage of the substrate material under the membrane was investigated. Eventually, a method and processing window could be defined that could produce blister-free parts. Full article
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Article
An Investigation on a Novel 3-RCU Flexible Micromanipulator
Micromachines 2020, 11(4), 423; https://doi.org/10.3390/mi11040423 - 17 Apr 2020
Cited by 4 | Viewed by 672
Abstract
A novel type of spatial three revolute-cylindrical-universal (3-RCU) flexible micro manipulator is designed based on flexible hinges, and analyzed by finite element analysis (FEA). The piezoelectric actuators are adopted as driving devices in this platform, a new lever amplification mechanism is designed as [...] Read more.
A novel type of spatial three revolute-cylindrical-universal (3-RCU) flexible micro manipulator is designed based on flexible hinges, and analyzed by finite element analysis (FEA). The piezoelectric actuators are adopted as driving devices in this platform, a new lever amplification mechanism is designed as its micro-displacement amplification mechanism, the workspace of the platform is enlarged, and the theoretical and simulation amplification ratios of the amplification mechanism are 3.056 and 2.985, respectively. The margin of error is just 2.3%. In space, the 3-RCU platform can realize the micro movement of three degrees of freedom. Also, the platform has a high carrying capacity, less motion loss, and the transmission efficiency is higher when the platform works. The decoupling performance, stress under extreme conditions and natural frequency of the platform are simulated by ANSYS Workbench software. A series of simulation analyses show the feasibility and security of the platform. The platform has good decoupling and working performance. The simulation results show that the platform has high simulation stiffness and high positioning accuracy. Full article
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Article
A Novel Micromachined Z-axis Torsional Accelerometer Based on the Tunneling Magnetoresistive Effect
Micromachines 2020, 11(4), 422; https://doi.org/10.3390/mi11040422 - 17 Apr 2020
Cited by 2 | Viewed by 672
Abstract
A novel micromachined z-axis torsional accelerometer based on the tunneling magnetoresistive effect is presented in this paper. The plane main structure bonded with permanent magnetic film is driven to twist under the action of inertial acceleration, which results in the opposite variation of [...] Read more.
A novel micromachined z-axis torsional accelerometer based on the tunneling magnetoresistive effect is presented in this paper. The plane main structure bonded with permanent magnetic film is driven to twist under the action of inertial acceleration, which results in the opposite variation of the magnetic field intensity. The variation of the magnetic field is measured by two differential tunneling magnetoresistive sensors arranged on the top substrate respectively. Electrostatic feedback electrodes plated on the bottom substrate are used to revert the plane main structure to an equilibrium state and realize the closed-loop detection of acceleration. A modal simulation of the micromachined z-axis tunneling magnetoresistive accelerometer was implemented to verify the theoretical formula and the structural optimization. Simultaneously, the characteristics of the magnetic field were analyzed to optimize the layout of the tunneling magnetoresistance accelerometer by finite element simulation. The plane main structure, fabricated with the process of standard deep dry silicon on glass (DDSOG), had dimensions of 8000 μm (length) × 8000 μm (width) × 120μm (height). A prototype of the micromachined z-axis tunneling magnetoresistive accelerometer was produced by micro-assembly of the plane main structure with the tunneling magnetoresistive sensors. The experiment results demonstrate that the prototype has a maximal sensitivity of 1.7 mV/g and an acceleration resolution of 128 μg/Hz0.5 along the z-axis sensitive direction. Full article
(This article belongs to the Section A:Physics)
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Article
The Effect of Streaming Potential and Viscous Dissipation in the Heat Transfer Characteristics of Power-Law Nanofluid Flow in a Rectangular Microchannel
Micromachines 2020, 11(4), 421; https://doi.org/10.3390/mi11040421 - 17 Apr 2020
Cited by 2 | Viewed by 641
Abstract
The non-Newtonian nanofluid flow becomes increasingly important in enhancing the thermal management efficiency of microscale devices and in promoting the exploration of the thermal-electric energy conversion process. The effect of streaming potential and viscous dissipation in the heat transfer characteristics of power-law nanofluid [...] Read more.
The non-Newtonian nanofluid flow becomes increasingly important in enhancing the thermal management efficiency of microscale devices and in promoting the exploration of the thermal-electric energy conversion process. The effect of streaming potential and viscous dissipation in the heat transfer characteristics of power-law nanofluid electrokinetic flow in a rectangular microchannel has been investigated to assist in the development of an energy harvesting system. The electroviscous effect caused by the streaming potential influences the hydrodynamical and thermal characteristics of flow. With the change in constitutive behavior of power-law nanofluid, the viscous dissipation effect is considered. The Poisson–Boltzmann equation, the modified Cauchy momentum equation, and the energy equation were solved. The temperature and heat transfer rate were analytically expressed for Newtonian nanofluid and numerically obtained for power-law nanofluid. The interactive influence of streaming potential, viscous dissipation, and hydrodynamical features of power-law nanofluid on the heat transfer characteristics were studied. The presence of streaming potential tends to reduce the dimensionless bulk mean temperature. The introduction of nanoparticles augments dimensionless temperature difference between channel wall and bulk flow, which decreases the heat transfer rate. The shear thinning nanofluid is more sensitive to the above effects. The temperature is a weak function of the flow behavior index. Full article
(This article belongs to the Section A:Physics)
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